1. Field of the Invention
The present invention relates to a flat panel display device, and more particularly, to a flat panel display device that may have an increased screen aperture and that may prevent brightness non-uniformity due to a voltage drop in a display region.
2. Discussion of the Background
Recently, various flat display devices have been developed to replace the conventional cathode ray tube (CRT). Generally, flat panel display devices are either emissive or non-emissive types. Emissive types include flat CRTs, plasma display panels, vacuum fluorescent displays, field emission displays, and inorganic/organic electro-luminescent (EL) displays, and non-emissive types include liquid crystal displays. The organic EL displays have drawn attention since they do not require a light source, such as a back light, and they may operate with low power consumption and high efficiency.
The organic EL display device emits light having a specific wavelength by energy generated from exitons, which are formed by electrons and holes that are injected through an anode and a cathode and recombine in an organic thin film. The organic EL display device is capable of operating with a low voltage, is thin and light, and has a wide viewing angle and a quick response time.
An organic EL unit of the organic EL display device may include a first electrode (an anode) formed in a stacking type on a substrate, an organic EL layer, and a second electrode (a cathode). The organic EL layer comprises an organic emitting layer (EML) that emits light by forming exitons. To increase the light emission efficiency, electrons and holes must be transferred to the organic EML. Hence, an electron transport layer (ETL) may be disposed between the cathode and the organic emitting layer, and a hole transport layer (HTL) may be disposed between the anode and the organic emitting layer. Also, a hole injection layer (HIL) may be disposed between the anode and the HTL, and an electron injection layer (EIL) may be disposed between the cathode and the ETL.
The organic EL display device may be a passive matrix (PM) or active matrix (AM) type according to its driving method. In the PM type, the anode and the cathode may be simply arranged in columns and rows, respectively, and a row driving circuit supplies scanning signals to the cathode one row at a time. Also, a column driving circuit supplies data signals to each pixel. On the other hand, the AM type controls signals inputted to each pixel using a thin film transistor (TFT) and is widely used for displaying animations since it may process a large number of signals.
However, in an organic/inorganic EL display device, and particularly in an AM type organic/inorganic EL display device, a ratio of a light emitting region to each pixel, that is, a pixel aperture, may be reduced due to the layout of a circuit unit and wirings.
FIG. 1A is a plan view showing a conventional organic EL display device.
The AM type organic EL display device of FIG. 1A has a predetermined display region 20, which includes an organic light emitting diode (OLED) on a transparent substrate 11, and a sealing unit 80 seals a sealing member (not shown), such as a metal cap, to seal the display region 20. The display region 20 comprises a plurality of pixels having an OLED and a TFT. A plurality of driving lines VDD 31 may be disposed in the display region 20. The driving lines 31, which supply power to the display region 20, are coupled with a terminal region 70 through a driving power supply line 32 disposed outside of the display region 20.
FIG. 1B is a magnified picture showing portion “A” of FIG. 1A. Here, the driving lines 31 must be thick and wide enough to prevent a voltage drop from occurring when supplying power to the display region 20. Consequently, the aperture ratio, which is an area ratio of a light emitting region with respect to each of the pixels decreases, which increases the to ratio of a dead space with respect to the overall display region, thereby reducing image quality.
Japanese Patent publication No. 2003-308031 discloses an organic EL display device structure in which power lines and gate lines are disposed parallel to each other to improve brightness. However, the effect of power line width on aperture ratio and the voltage drop problem that may occur with an increased screen size are not addressed.